102 Welding. resorted to, the crystallised portion will be left weak and little better than cast iron. This should be carefully noted in making connecting rods of steam engines, or indeed any article the break- ing of which might cause danger to life. Welding.ŚWrought iron cannot be cast,* but it can be welded without difficulty; that is, it may be joined piece to piece by heating and hammering, and work of great intricacy may thus be formed. The welding temperature for wrought iron is reached at about 2800░ Fahrenheit, and the two pieces to be welded are heated to this temperature, which is detected by the iron beginning to throw out sparks. Two points have to be noticed. The iron should be, if possible, drawn out so that a scarf may be made, when welded; this is shewn at A, Fig. 103, and, as will be seen, a greater surface for welding is thereby presented. But, if it be drawn out too fine, it will burn away when put into the fire for the welding heat, and to prevent this it should be left rather thick at the ends, as at B ; the lump may be easily levelled afterwards. The two pieces to be welded should both be at their proper heat at the same time, which the smith ensures by changing their positions in the fire, so as to advance the one or retard the other. Withdrawing, he sprinkles them with sand, which forms a siliceous film or flux, and prevents scale by oxidation. Putting them now together, the smith gives one or two blows to fix them, and he and the striker then finish by rapid alternating blows. If the flux be carefully expelled and the joint well hammered while hot, the bar will be nearly as strong there as at any other section. Borax is used as a flux in steel welding. (See Appendices /. and Iff., pp. 748 and 917.) The scarf weld is the one most commonly practised, but the fork weld at c, Fig. 103, is often introduced for large work on account of its greater security. Having thus briefly mentioned the operations of heating and welding, we shall now proceed to describe the forging of a few objects. The making of a Bolt with hexagonal head is shewn in Fig. 104. A round bar A is taken, of suitable length; it is heated at one end, and jumped or upset, namely, is lifted by * See note at end of Chapter III.